Process for degrading plastic products

ABSTRACT

The present invention relates to processes for degrading plastic products and the uses thereof. The processes of the invention particularly comprise a step of amorphizing a plastic product prior to a step of depolymerization. The processes of the invention are particularly useful for degrading a plastic product comprising polyethylene terephthalate and/or polylactic acid. The invention also relates to a method of producing monomers and/or oligomers from a plastic product comprising at least one polyester, particularly polyethylene terephthalate and/or polylactic acid, comprising submitting the plastic product both to an amorphization step and to a depolymerization step.

CROSS-REFERENCE TO RELATED APPLICATION

This application is the U.S. national stage application of InternationalPatent Application No. PCT/EP2017/062028, filed May 18, 2017.

The present invention relates to processes for degrading plasticproducts and the uses thereof. The processes of the inventionparticularly comprise a step of amorphizing a plastic product prior to astep of depolymerization. The processes of the invention areparticularly useful for degrading a plastic product comprisingpolyethylene terephthalate and/or polylactic acid. The invention alsorelates to a method of producing monomers and/or oligomers from aplastic product comprising at least one polyester, particularlypolyethylene terephthalate and/or polylactic acid, comprising submittingthe plastic product both to an amorphization step and to adepolymerization step.

BACKGROUND

Plastics are inexpensive and durable materials, which can be used tomanufacture a variety of products that find use in a wide range ofapplications. As a consequence, the production of plastics has increaseddramatically over the last decades. Moreover, more than 50% of theseplastics are used for single-use disposable applications, such aspackaging, agricultural films, disposable consumer items or forshort-lived products that are discarded within a year of manufacture.Because of the durability of the polymers involved, substantialquantities of plastics are piling up in landfill sites and in naturalhabitats worldwide, generating increasing environmental problems. Evendegradable and biodegradable plastics may persist for decades dependingon local environmental factors, like levels of ultraviolet lightexposure, temperature, presence of suitable microorganisms, etc.

Different solutions have been studied to reduce environmental andeconomic impacts correlated to the accumulation of plastic, from plasticdegradation to plastic recycling, including reprocessing the degradedplastic in new plastic material.

As an example, in recent years, polyethylene terephthalate (PET), anaromatic polyester produced from terephthalic acid and ethylene glycol,has been widely employed in the manufacture of several products forhuman consumption, such as food and beverage packaging (e.g.: bottles,convenience-sized soft drinks, pouches for alimentary items) ortextiles, fabrics, rugs, carpets, etc.

In parallel, PET is the most closed-loop recycled plastic. Generallyspeaking, PET wastes are subjected to successive treatments leading torecycled PET (rPET). PET wastes (mainly bottles) are collected, sorted,pressed into bales, crushed, washed, chopped into flakes, melted andextruded in pellets and offered for sale. Then, these recycled PET maybe used to create fabrics for the clothing industry or new packagingsuch as bottles or blister packs, etc.

However, such plastic recycling processes are adapted to plastic itemscontaining only PET, and thus need a prior extensive sorting. Suchplastic recycling processes thus lead to downgrading applications andare also expensive, so that the recycled products are generallynon-competitive compared to virgin plastic.

Another potential process for recycling plastic consists of chemicalrecycling allowing recovering the chemical constituents of the polymer.The resulting monomers, after purification, may be used tore-manufacture plastic items or to make other synthetic chemicals.However, up to now, such recycling process has only been performed onsorted or partially sorted polymers and is not efficient on raw plasticproducts that may comprise a mix of different polymers.

Thus, a need exists for an improved process for degrading plasticproducts that does not require preliminary sorting and/or expensivepretreatments and that may be used with industrial yield.

SUMMARY OF THE INVENTION

The present invention provides novel methods for degrading plasticproducts containing polyesters, which comprise a step of amorphizing theplastic product and a step of depolymerization. Advantageously, theamorphization step allows to decrease the degree of crystallinity of apolyester of the plastic product and thereby favors subsequentdepolymerization. By combining amorphization and depolymerization, ahigh level of degradation is obtained without sorting and underindustrial conditions. The methods of the invention are particularlyuseful for degrading plastic products containing polyethyleneterephthalate.

In this regard, it is an object of the invention to provide a processfor degrading a plastic product containing at least one polyester,comprising the steps of:

a. Amorphizing at least partially at least one polyester of the plasticproduct; and

b. Depolymerizing said at least partially amorphized polyester of theplastic product.

It is also another object of the invention to provide a method forproducing monomers and/or oligomers from a plastic product containing atleast one polyester, comprising submitting the plastic product to anamorphization step to amorphize at least partially a polyester of theplastic product, and to a subsequent depolymerization step todepolymerise said at least partially amorphized polyester of the plasticproduct. According to the invention, the depolymerization step is abiological depolymerization, wherein the plastic product is exposed to adepolymerase. It is a further object of the invention to provide amethod for recycling a plastic product comprising at least onepolyester, comprising subjecting successively said at least onepolyester to amorphization and depolymerization, and recovering monomersand/or oligomers.

It is also an object of the invention to provide a method for treating aplastic product comprising at least one polyester, wherein the plasticproduct is subjected to amorphization and depolymerization.

In a particular embodiment, the amorphization step comprises submittingthe plastic product to a temperature above the crystallizationtemperature (Tc), preferably above the melting temperature (Tm) of apolyester of the plastic product.

In addition, the amorphization step comprises submitting the plasticproduct to shear stress. In a particular embodiment, the amorphizationstep further comprises, upon heating, submitting the plastic product toa temperature below the glass transition temperature (Tg) of saidpolyester.

In a particular embodiment, the process comprises a subsequentbiological depolymerization step, wherein the plastic product iscontacted with a depolymerase and/or a microorganism expressing andexcreting a depolymerase. Advantageously, the depolymerase is selectedfrom cutinases, lipases, proteases, carboxylesterases and esterases,preferably from cutinases and proteases.

It is therefore an object of the invention to provide a process fordegrading a plastic product containing at least one polyester,comprising the steps of:

-   -   a) Amorphizing at least partially at least one polyester of the        plastic product by submitting successively the plastic product        to a temperature above the crystallization temperature (Tc),        preferably above the melting temperature (Tm) of a polyester of        the plastic product and to a temperature below the glass        transition temperature (Tg) of said polyester; and    -   b) Depolymerizing said at least partially amorphized polyester        of the plastic product by contacting the plastic product of        step a) with a depolymerase and/or a microorganism expressing        and excreting a depolymerase.

Advantageously, the plastic product comprises semi-crystallinepolyesters, preferably polyethylene terephthalate and/or polylacticacid.

It is a further object of the invention to provide a process fordegrading a plastic product containing PET, comprising the steps of:

a. Amorphizing at least partially PET of the plastic product; and

b. Depolymerizing PET of the plastic product,

wherein the amorphizing step comprises exposing the plastic product to atemperature of or above 245° C., preferably comprised between 250° C.and 300° C., then exposing the plastic product to a temperaturecomprised between 4° C. and 65° C., and/or the depolymerising stepcomprises submitting the plastic product to a cutinase.

These and the other objects and embodiments of the invention will becomemore apparent after the detailed description of the invention, includingpreferred embodiments thereof given in general terms.

LEGEND TO THE FIGURES

FIG. 1: Depolymerization of Volvic® bottles before (VB1) and after anamorphization step according to the invention (VB2, VB3). The initialrate of enzymatic depolymerization was improved 8.2 times and 9.8 timesfor amorphized samples VB2 and VB3 respectively, in comparison withnon-treated Volvic® bottle (sample VB1). At the end of the reaction, 88%and 84% of amorphized samples VB2 and VB3 were enzymatically degraded,respectively, whereas only 12% of crystalline Volvic® sample VB1 wereenzymatically degraded.

FIG. 2: Depolymerization of Volvic® bottles before (VB1) and after anamorphization step according to the invention (VB4, VB5, VB6). Theinitial rate of enzymatic depolymerization was improved 3.6 times, 4.8times and 8.4 times for amorphized samples VB4, VB5 and VB6respectively, in comparison with non-treated Volvic® bottle (sampleVB1). At the end of the reaction, 82%, 94% and 47% of amorphized samplesVB4, VB5 and VB6 were enzymatically degraded, respectively, whereas only12% of crystalline Volvic® sample VB1 were enzymatically degraded.

FIG. 3: Depolymerization of milk bottles before (MB1) and after anamorphization step according to the invention (MB2, MB3, MB4). Theinitial rate of enzymatic depolymerization was improved 3.2 times, 4.6times and 10 times for amorphized samples MB3, MB2 and MB4 respectively,in comparison with non-treated milk bottle (sample MB1). At the end ofthe reaction, 86%, 88% and 89% of amorphized samples MB3, MB2 and MB4were enzymatically degraded, respectively, whereas only 33% ofcrystalline milk bottle sample MB1 were enzymatically degraded.

FIG. 4: Depolymerization of Cristaline™ water bottles before (CB1) andafter amorphization according to the invention (CB2). At the end of thereaction 90.5% of amorphized Cristaline™ bottle sample CB2 wasenzymatically degraded, whereas only 18% of crystalline Cristaline™bottle sample CB1 were enzymatically degraded.

DETAILED DESCRIPTION OF THE INVENTION Definitions

The present disclosure will be best understood by reference to thefollowing definitions.

Within the context of the invention, the terms “plastic article” or“plastic product” are used interchangeably and refer to any item orproduct comprising at least one polymer, such as plastic sheet, tube,rod, profile, shape, massive block, fiber, etc. Preferably, the plasticarticle is a manufactured product, such as rigid or flexible packaging,agricultural films, bags and sacks, disposable items or the like, carpetscrap, fabrics, textiles, etc. The plastic article may containadditional substances or additives, such as plasticizers, minerals,organic fillers or dyes. In the context of the invention, the plasticarticle may comprise a mix of semi-crystalline and/or amorphous polymersand/or additives.

A “polymer” refers to a chemical compound or mixture of compounds whosestructure is constituted of multiple repeating units (i.e. “monomers”)linked by covalent chemical bonds. Within the context of the invention,the term “polymer” includes natural or synthetic polymers, comprising asingle type of repeating unit (i.e., homopolymers) or different types ofrepeating units (i.e., block copolymers and random copolymers). As anexample, synthetic polymers include polymers derived from petroleum oil,such as polyolefins, aliphatic or aromatic polyesters, polyamides,polyurethanes and polyvinyl chloride. Natural polymers include lignin,polysaccharides, such as cellulose, hemi-cellulose, starch, andpolyhydroxyalkanoates and derivatives thereof.

According to the invention, “oligomers” refer to molecules containingfrom 2 to about 20 monomer units. As an example, oligomers retrievedfrom PET include methyl-2-hydroxyethyl terephthalate (MHET) and/orbis(2-hydroxyethyl) terephthalate (BHET) and/or 2-hydroxyethyl benzoate(HEB) and/or dimethyl terephthalate (DMT). As another example, oligomersof lactic acid may be retrieved from PLA.

Within the context of the invention, the term “polyester” refers to apolymer that contain the ester functional group in their main chain.Ester functional group is characterized by a carbon bound to three otheratoms: a single bond to a carbon, a double bond to an oxygen, and asingle bond to an oxygen. The singly bound oxygen is bound to anothercarbon. According to the composition of their main chain, polyesters canbe aliphatic, aromatic or semi-aromatic. Polyester can be homopolymer orcopolymer. As an example, polyethylene terephthalate is a semi-aromaticcopolymer composed of two monomers, terephthalic acid and ethyleneglycol.

In the context of the invention, “crystalline polymers” or“semi-crystalline polymers” refer to partially crystalline polymerswherein crystalline regions and amorphous regions coexist. The degree ofcrystallinity of a semi-crystalline polymer may be estimated bydifferent analytical methods and typically ranges from 10 to 90%. Forinstance, Differential Scanning calorimetry (DSC) or X-Ray diffractionmay be used for determining the degree of crystallinity of polymers.Other techniques are also suited for estimating with less reliabilitypolymer's crystallinity, such as Small Angle X-ray Scattering (SAXS) andInfrared Spectroscopy. In the present disclosure, the degrees ofcrystallinity disclosed correspond to degrees of crystallinity measuredwith DSC. More particularly, the DSC experiments were conducted asfollow: a small quantity of the sample (several mg) is heated at aconstant heating rate, from ambient or sub-ambient temperature to a hightemperature that is higher than the Tm of the polyester. The heat flowdata is collected and plotted against temperature. The degree ofcrystallinity Xc (%) is calculated as:

${{Xc}(\%)} = {\frac{\left( {{\Delta\;{Hf}} - {\Delta\;{Hcc}}} \right)}{{wt}*\Delta\;{Hf}\; 100\%} \times 100\%}$

where

ΔH_(f) is the enthalpy of melting that can be determined by integratingthe endothermic melting peak,

ΔH_(cc) is the enthalpy of cold crystallization and determined byintegrating the exothermic cold crystallization peak,

w_(t) the weight fraction of polyester in the plastic, and

ΔH_(f,100%) is the enthalpy of melting for a fully crystalline polymerand can be found in literature.

As an example, ΔH_(f,100%) of PET is taken from literature as 125.5 J/g(Polymer Data Handbook, Second Edition, Edited by James E. Mark, OXFORD,2009). According to the literature, ΔH_(f,100%) of PLA is equal to 93J/g (Fisher E. W., Sterzel H. J., Wegner G., Investigation of thestructure of solution grown crystals of lactide copolymers by means ofchemical reactions, Kolloid Zeitschrift & Zeitschrift fur Polymere,1973, 251, p 980-990).

As used herein, the terms “amorphization” or “amorphizing” are usedinterchangeably to refer to a step decreasing the degree ofcrystallinity of a given polymer compared to the degree of crystallinitybefore the amorphizing step. Preferably, the amorphizing step allows todecrease the crystallinity of a target polymer of at least 5%, 10%, 15%,20%, 25%, 30%, 35%, 40%, 50%, 60%, 70%, 80%, 90% compared to its degreeof crystallinity before amorphization. Advantageously, the amorphizationstep, in the meaning of the invention, leads to a polymer in the plasticproduct with at most 30%, preferably at most 25%, more preferably atmost 20% of crystallinity, even more preferably at most 15%. Preferably,the amorphization step allows to decrease the crystallinity of a targetpolymer of at least 5%, 10%, 20%, 30%, 40% compared to the degree ofcrystallinity before the amorphizing step, leading to a polymer with atmost 25%, preferably at most 20% and more preferably at most 15% ofcrystallinity.

A “degrading process” in relation to a plastic article refers to aprocess by which at least one polymer of said plastic article isdegraded in smaller molecules, such as monomers, oligomers, water and/orcarbon dioxide.

In the context of the invention, “Tg”, “Tc”, “Tcc”, and “Tm”respectively refer to the glass transition temperature, thecrystallization temperature, the cold crystallization temperature andthe melting temperature of a polymer. Such temperatures may be estimatedby different analytical methods well known by the person skilled in theart. For instance, Differential Scanning calorimetry (DSC) orDifferential thermal analysis (DTA) may be used for determining the Tg,Tc, Tcc, and Tm of polymers. In the present disclosure, Tg, Tc, Tcc, andTm of polymers disclosed correspond to temperatures measured with DSC.

Amorphization Step

The inventors have shown that it is possible to improve thedegradability of a plastic product comprising polyesters by submittingthe plastic product to conditions favouring amorphization of a givenpolyester prior to a depolymerisation thereof. The amorphizing stepallows to break at least partially the crystalline structure of at leastone polyester of the plastic product.

In a particular embodiment, the amorphization step comprises submittingthe plastic product to a temperature at which the plastic product is ina partially or totally molten state.

It is therefore an object of the invention to provide a process ofdegrading a plastic article, wherein the step of amorphizing comprisessubmitting the plastic product to a temperature above thecrystallization temperature (Tc) of a polyester of the plastic product,preferably at or above the melting temperature (Tm) of said polyester.Particularly, the plastic product is submitted to a temperaturecorresponding to the Tm of a polyester of the plastic product. Even morepreferably, the plastic product is submitted to a temperaturecorresponding to the Tm+5 to 25° C., preferably Tm+10 to 25° C., morepreferably Tm+15 to 25° C., such as Tm+20° C. of a polyester of theplastic product. In another embodiment, the plastic product is submittedto a temperature corresponding to the Tm+25 to 50° C. In anotherpreferred embodiment, the plastic product is submitted to a temperaturecorresponding to Tm+50° C. or above.

According to the invention, the plastic product may comprise differentpolyesters. In such case, the plastic product is advantageouslysubmitted to a temperature at or above the Tc or at or above the Tm ofthe target polyester, i.e.; for which a depolymerization is intended.Alternatively, the plastic product is submitted to a temperature at orabove the highest Tc or Tm of the polyesters contained in the plasticproduct. Such embodiment may lead to the amorphization of all polyesterscontained in the plastic product.

In a particular embodiment, the plastic product further comprisesthermoplastic polymers other than a polyester. In such a case, theplastic product may be alternatively submitted to a temperature at orabove the Tc or at or above the Tm of the target polyester, or to atemperature above the highest Tc or Tm of the thermoplastic polymerscontained in the plastic product.

The temperature of the amorphizing step can be adapted by a personskilled in the art depending on the targeted polyester. Generallyspeaking, the plastic product shall be subjected to the heat treatmentfor a period of time sufficient to obtain amorphization of the targetedpolyester. For instance, such duration may be comprised between 10seconds and several minutes, depending on the temperature and/or theplastic product.

In a particular embodiment, the plastic product comprises PET, and theamorphizing step comprises submitting the plastic product to atemperature above 170° C., preferably at or above 245° C. and morepreferably to a temperature between 250° C. and 300° C. Even morepreferably, the plastic product comprising PET is submitted to atemperature between 260° C. and 280° C. In another embodiment, theplastic product comprising PET is submitted to a temperature at or above300° C., preferably between 300° C. and 320° C.

In another particular embodiment, the plastic product comprises PLA, andthe amorphizing step comprises submitting the plastic product to atemperature above 110° C. and more preferably at or above 145° C. In aparticular embodiment, the plastic product comprises PLLA, and theamorphizing step comprises submitting the plastic product to atemperature at or above 180° C.

In another embodiment, the plastic product comprises stereocomplex PLAand the amorphizing step comprises submitting the plastic product to atemperature at or above 230° C.

In a preferred embodiment, the amorphization step comprises submittingthe plastic product to both a shear stress and to a temperature abovethe Tc of a polyester of the plastic product, preferably at or above theTm of said polyester. The heating and shear stress are preferablyperformed at the same time to increase amorphization.

In a particular embodiment, the step of amorphizing may furthercomprise, following the heating of the plastic product, a cooling ofsaid plastic product, in order to fix the plastic product into theamorphized state. Advantageously, the cooling is performed immediatelyafter the heating.

In a particular embodiment, the cooling is performed by submitting theheated plastic product to a temperature below the glass transitiontemperature (Tg) of a polyester of the plastic product.

In another particular embodiment, the cooling is performed by submittingthe heated plastic product to a temperature below the Tc of a polyesterof the plastic product. This particular embodiment is particularlyadapted to PBAT for instance or to any polyester whose Tg is inferior to20° C. Alternatively, the cooling is performed by submitting the heatedplastic product to a temperature that is at least 20° C. lower than theTc, preferably at least 30° C., 40° C., 50° C.

In a particular embodiment, the cooling is performed by submitting theplastic product to room temperature (i.e.; 25° C.+/−5° C.). In anotherembodiment, the cooling is performed by submitting the plastic productto a temperature of about 10° C., preferably about 5° C.

In a particular embodiment, the plastic product is submitted to acooling temperature subsequently to the heating phase, particularly lessthan 1 minute, preferably less than 30 seconds, more preferably lessthan 20 seconds, even more preferably less than 10 seconds after theheating phase.

As an example, the cooling may be performed by immersing the plasticproduct into a liquid at a temperature below the Tg of a givenpolyester. For instance, the plastic product is immersed into a liquidat room temperature, more preferably below room temperature. Morepreferably, the plastic article is immersed in a cold liquid, whosetemperature is below 14° C., preferably below 10° C. or below 5° C. In aparticular embodiment, the plastic product is immersed into cold water,such as water at or below 5° C.

Alternatively, the cooling may be obtained by submitting the plasticproduct to cold air. As another example, such plastic article may becooled by cooling air system.

Alternatively or in addition, the cooling may be performed using anunderwater pelletizer where polymer is directly cut in cold water usinga thermoregulated water system, the plastic is pelletized into finepellets. Particularly, such underwater granulator may be fixed in thehead of the extruder used for submitting the plastic product to theprior heating, such as the ones sold by Gala Industries® or ECONUnderwater Pelletizing System®. Preferably, the cooling may be performedusing a microgranulation underwater pelletizer leading to microgranulates or mini pellets with a size below 1 mm. Such processadvantageously permits to remove the step of grinding betweenamorphization and depolymerization.

More generally, any method suitable for rapidly reducing the temperatureof the plastic product may be used.

According to the invention, the plastic product may comprise differentpolyesters. In such case, the plastic product is advantageouslysubmitted to a temperature below the Tc or the Tg of the polyester forwhich the depolymerization is intended. Alternatively, the plasticproduct is submitted to a temperature below the lowest Tc or Tg of thepolyesters contained in the plastic product. When such polyester has aTg below 0° C., the plastic product is advantageously submitted to atemperature below room temperature, preferably below 20° C. When suchpolyester has a Tg below 20° C., the plastic product is advantageouslysubmitted to a temperature below room temperature, preferably below 20°C.

In another embodiment, the plastic product further comprisesthermoplastic polymers other than polyester. In such a case, the plasticproduct is alternatively submitted to a temperature below the Tc or theTg of the polyester for which the depolymerization is intended or to atemperature below the lowest Tc or Tg of the thermoplastic polymerscontained in the plastic product. In the case where at least onethermoplastic polymer of the plastic product has a Tg inferior to 20°C., the plastic product may be submitted to a temperature below roomtemperature, preferably below 20° C.

In a particular embodiment, the step of amorphizing further comprisesadding at least one degrading agent. Examples of degrading agentsinclude, without limitation, water, monomers, alcohol, metal alkoxides,plasticizers, etc. Preferably, such degrading agents may be added duringthe heating phase of the plastic product and/or the shear stress phaseof the plastic product.

Preferably, the step of amorphization comprises at least addition ofwater. Alternatively or in addition, monomers of a polyester of theplastic product are added during the step of amorphization. Preferably,monomers are selected from monomers of the targeted polyester (i.e.: forwhich a depolymerization is intended). In a particular embodiment,monomers of PET such as monoethylene glycol and/or terephthalic acidand/or isophthalic acid are added during the step of amorphization of aplastic article comprising PET. Particularly, such monomers are addedduring the heating phase of the plastic article.

Preferably, such degrading agents are added at a concentration below 20%of the total mass (i.e. plastic product and degrading agents),preferably at a concentration between 0.05 and 10%, more preferablybetween 0.05 and 5%, before to be submitted to the amorphization step.In another embodiment, such degrading agents are added at aconcentration between 0.1 and 10%, more preferably between 0.1 and 5%,before to be submitted to the amorphization phase.

In a particular embodiment, water is added during the heating phase ofthe plastic article at a concentration above 5% of the total mass,preferably between 10 and less than 20%. Alternatively or in addition,monomers are added during the heating phase of the plastic article at aconcentration below 10% of the total mass, preferably below 5%, 4%, 3%,2%, 1%.

In a particular embodiment, the amorphization step is performed using anextruder. The extruder allows to submit a plastic product both to agiven temperature and to shear stress, simultaneously or sequentially.It is also possible to add degrading agent(s) in the extruder, ifrequired. The extruder may further allow to cool the plastic product.Accordingly, the use of an extruder, such as single-screw extruders,multi-screw extruders of either co-rotating or counter-rotating design,planetary roller extruder, dispersive kneaders, reciprocatingsingle-screw extruder (co-kneaders), mini extruder or internal mixer maybe of particular interest to implement the amorphization step.Preferably, an underwater pelletizer producing mini pellets under 1 mmis fixed in the head of the extruder to allow the production of plasticpellets with desired size and to replace the potential step of grindingneeded before depolymerisation.

Amorphization may also be performed by implementing any process allowingto break at least partially the crystalline structure of at least onepolyester of the plastic product.

Alternatively, the amorphization step may be carried out in a reactor,or via atomization of the polyester, or solubilization of the polyesterin a solvent, or plasma treatment, or electronic or atomic irradiationor cryogenic mechanical attrition (Schexnaydre et al, 2008), or anytechniques known by a person skilled in the art.

Depolymerization Step

According to the invention, the degrading process comprises, followingthe amorphizing step, a step of depolymerization. According to apreferred embodiment, the depolymerizing step targets at least onepolyester targeted by the prior amorphizing step.

The depolymerizing step may comprise a chemical depolymerization and/ora biological depolymerization, preferably, at least a biologicaldepolymerization.

Accordingly, in a particular embodiment, the degrading process of theinvention comprises contacting the plastic product with a depolymerase(i.e., an enzyme). Preferably, the depolymerase is able to degrade atleast one polyester of the plastic product, preferably at least apolyester that has been previously amorphized by the amorphizing step.

The depolymerase is advantageously selected from the group consisting ofa cutinase, a lipase, a protease, a carboxylesterase, ap-nitrobenzylesterase, an esterase, a scl-PHA depolymerase, a mcl-PHAdepolymerase, a PHB depolymerase. In a particular embodiment, theplastic product is contacted with at least two different depolymerases.

In a particular embodiment, the plastic product comprises PET, and thedepolymerase is a cutinase, preferably selected from Thermobifidacellulosityca, Thermobifida halotolerans, Thermobifida fusca,Thermobifida alba, Bacillus subtilis, Fusarium solani pisi, Humicolainsolens, Sirococcus conigenus, Pseudomonas mendocina and Thielaviaterrestris, or any functional variant thereof. In another embodiment,the cutinase is selected from a metagenomic library such as LC-Cutinasedescribed in Sulaiman et al., 2012 or any functional variant thereof. Inanother particular embodiment, the depolymerase is a lipase preferablyselected from Ideonella sakaiensis. In another particular embodiment,the depolymerase is a cutinase selected from Humicola insolens, such asthe one referenced A0A075B5G4 in Uniprot or any functional variantthereof. In another embodiment, the depolymerase is selected fromcommercial enzymes such as Novozym 51032 or any functional variantthereof.

In a particular embodiment, the plastic product comprises PLLA, and thedepolymerase is a protease, preferably selected from Amycolatopsis sp.,Amycolatopsis orientalis, proteinase K from Tritirachium album,Actinomadura keratinilytica, Laceyella sacchari LP175, Thermus sp. orany commercial enzymes known for degrading PLA such as Savinase®,Esperase®, Everlase® or any functional variant thereof.

In another particular embodiment, the plastic product comprises PDLA,and the depolymerase is a cutinase or a lipase preferably selected fromCLE from Cryptococcus sp., lipase PS from Burkholderia cepacia,Paenibacillus amylolyticus TB-13, Candida Antarctica, Rhiromucor miehei,Saccharomonospora viridis, Cryptococcus magnus or any commercial enzymesknown for degrading PLA such as Savinase®, Esperase®, Everlase® or anyfunctional variant thereof.

The enzyme may be in soluble form, or on solid phase such as powderform. In particular, it may be bound to cell membranes or lipidvesicles, or to synthetic supports such as glass, plastic, polymers,filter, membranes, e.g., in the form of beads, columns, plates and thelike. The enzyme may be in an isolated or purified form. Preferentially,the enzymes of the invention are expressed, derived, secreted, isolated,or purified from microorganisms. The enzymes may be purified bytechniques known per se in the art, and stored under conventionaltechniques. The enzymes may be further modified to improve e.g., theirstability, activity and/or adsorption on the polymer. For instance, theenzymes are formulated with stabilizing and/or solubilizing components,such as water, glycerol, sorbitol, dextrin, including maltodextrineand/or cyclodextrine, starch, propanediol, salt, etc.

In another embodiment, the plastic product is contacted with amicroorganism that expresses and excretes the depolymerase. In thecontext of the invention the enzyme may be excreted in the culturemedium or towards the cell membrane of the microorganism wherein saidenzyme may be anchored. Said microorganism may naturally synthesize thedepolymerase, or it may be a recombinant microorganism, wherein arecombinant nucleotide sequence encoding the depolymerase has beeninserted, using for example a vector. For example, a nucleotidemolecule, encoding the depolymerase of interest is inserted into avector, e.g. plasmid, recombinant virus, phage, episome, artificialchromosome, and the like. Transformation of the host cell as well asculture conditions suitable for the host are well known to those skilledin the art.

The recombinant microorganisms may be used directly. Alternatively, orin addition, recombinant enzymes may be purified from the culturemedium. Any commonly used separation/purification means, such assalting-out, gel filtration, hydrophobic interaction chromatography,affinity chromatography or ion exchange chromatography may be used forthis purpose. In particular embodiments, microorganisms known tosynthesize and excrete depolymerases of interest may be used.

According to the invention, several microorganisms and/or purifiedenzymes and/or synthetic enzymes may be used together or sequentially todepolymerize different kinds of polymers contained in a same plasticarticle or in different plastic articles.

Advantageously, the microorganism of the invention exhibits a modifiedmetabolism in order to prevent the consumption of the monomers and/oroligomers obtained from the degraded polymers. For example, themicroorganism is a recombinant microorganism, wherein the enzymesdegrading said monomers and/or oligomers have been deleted or knockedout. Alternatively, the process of the invention may be performed in aculture medium containing at least one carbon source usable by themicroorganism so that said microorganism preferentially consumes thiscarbon source instead of the monomers and/or oligomers.

Advantageously, the plastic article is contacted with a culture mediumcontaining the microorganisms, glucose or the like as a carbon source,as well as an available nitrogen source, including an organic nitrogensource (e.g., peptone, meat extract, yeast extract, corn steep liquor)or an inorganic nitrogen source (e.g., ammonium sulfate, ammoniumchloride). If necessary, the culture medium may further containinorganic salts (e.g., sodium ion, potassium ion, calcium ion, magnesiumion, sulfate ion, chlorine ion, phosphate ion). Moreover, the medium mayalso be supplemented with trace components such as vitamins and aminoacids.

In a particular embodiment, the depolymerase is used under conditionsfavoring its adsorption on the plastic article, so that the polymer ofthe plastic article is more efficiently depolymerized up to monomersand/or oligomers. More particularly, the depolymerase may be a mutatedenzyme having improved affinity for the polymer of the plastic particlecompared to a wild-type enzyme. Alternatively, the depolymerase may beused with plastic-binding proteins or binding modules that enhance thebinding between the depolymerase and the polymer of the plastic article.

The time required for depolymerization of at least one polymer of theplastic article may vary depending on the plastic article and itspolymer itself (i.e., nature and origin of the plastic article, itscomposition, shape, molecular weight, etc.), the type and amount ofmicroorganisms/enzymes used, as well as various process parameters(i.e., temperature, pH, additional agents, etc.). More generally, thetemperature is maintained below an inactivating temperature, whichcorresponds to the temperature at which the depolymerase is inactivatedand/or the recombinant microorganism does no more synthesize thedepolymerase. In a particular embodiment, the temperature is maintainedbelow the Tg of the target polyester to be depolymerized.Advantageously, the pH is adjusted for improving the process efficiencyaccording to several factors, including the targeted polyester, thesolubility of the targeted monomers/oligomers and/or the development ofcoproducts during the process. In a particular embodiment, the pH isadjusted to be maintained at the optimal pH of the depolymerase. Oneskilled in the art may easily adapt the process parameters to theplastic articles and/or depolymerases.

In a particular embodiment, the plastic product comprises PET, and theprocess is implemented at a temperature comprised between 20° C. and 90°C., preferably between 30° C. and 80° C., more preferably between 40° C.and 70° C., more preferably between 50° C. to 70° C., even morepreferably between 60° C. to 70° C. Furthermore, the process ispreferably implemented at a pH between 5-11, preferably between 7-9,more preferably between 7-8.5, even more preferably between 7-8.Advantageously, the process is performed under mixing, preferably underagitation, more preferably under vertical agitation with rotation speedpreferably comprised between 30 rpm and 2000 rpm, in order to favorcontact between the depolymerase and the plastic product.

In a particular embodiment, the plastic product comprises PLA, and theprocess is implemented at a temperature comprised between 20° C. and 90°C., preferably between 20° C. and 60° C., more preferably between 30° C.and 55° C., more preferably from 40° C. to 50° C., even more preferablyat 45° C. Furthermore, the process is preferably implemented at a pHbetween 5-11, preferably between 7-10, more preferably between 8.5-9.5,even more preferably between 8-9. In another particular embodiment, theprocess may be preferably implemented at a pH between 7 and 8. Oneskilled in the art may easily adapt the pH to the PLA-depolymerase.Advantageously, the process is performed under agitation, preferablycomprised between 30 rpm and 2000 rpm, in order to favor contact betweenthe depolymerase and the plastic product.

Additional Optional Steps

In a particular embodiment, the degrading process may comprise apreliminary depolymerising step, performed before the step ofamorphization. Preferably, after this preliminary depolymerising step,the non-depolymerized polymers are recovered before to perform theamorphization step.

In a particular embodiment, the degrading process may comprise apretreatment step to modify mechanically and/or physically and/orchemically and/or biologically the plastic product, said pretreatmentstep being preferably performed before the amorphizing step and/orbefore the depolymerising step.

For instance, the pretreatment can physically change the structure ofthe plastic product, so as to increase the surface of contact betweenthe polymers and the enzymes and/or to facilitate the amorphizationstep. Alternatively or in addition, the pretreatment allows to decreasethe microbial charge coming from wastes.

In a particular embodiment, the plastic article is transformed into anemulsion or a powder, which is added to a liquid medium containing themicroorganisms and/or enzymes. Alternatively, the plastic article may bemechanically ground, granulated, pelleted, etc. by cutting, impact,crushing, grinding, fractionation, cryogenic grinding, or the like, toreduce the size and modify the shape of the material prior to besubmitted to amorphization and/or to be added to a liquid mediumcontaining the microorganisms and/or enzymes. The mechanicalpretreatment can also be a sonication, a centrifugation, a shear, acollisop, a high-pressure homogenizer, a maceration or a liquefactionwith a rotary drum, a screw press, a disc screen shredder, or a pistonpress.

Alternatively or additionally, a thermal pretreatment can be applied,using for example microwaves. Such thermal pretreatment allowsdisinfection, pasteurization or sterilization of the plastic product.

In another particular embodiment, the plastic product is chemicallypretreated to modify its structure and increase the surface of contactbetween the polymers and the enzymes. A basic, acidic, or ionic liquid,as well as a solvent, can be used. An ozonation can also be implemented.

In a particular embodiment, the plastic article may also be sorted,washed, disinfected, sterilized and/or biologically cleaned prior todegradation.

According to the invention, several pre-treatments may be combined.

In a preferred embodiment, the plastic product containing PET issubmitted to a cryogenic grinding, freezer milling, freezer grinding, orcryomilling before the depolymerization step. Preferably, the plasticarticle is crushed or grinded before the amorphization step and/orbefore the depolymerization step. Particularly, the plastic product maybe physically transformed into film, flakes, powders, pellets or fibers.

Even more preferably, the amorphization step is performed using anextruder and an underwater pelletizer leading to micro granules below 1mm, such that no cryogenic grinding is needed before thedepolymerization step.

Plastic Articles

The inventors have developed a degrading process for degrading plasticarticles containing polyesters. The process of the invention may beadvantageously used with plastic articles from plastic waste collectionand/or post-industrial waste. More particularly, the process of theinvention may be used for degrading domestic plastic wastes, includingplastic bottles, plastic bags and plastic packaging, soft and/or hardplastics, even polluted with food residues, surfactants, etc.Alternatively, the process of the invention may be used for degradingplastic fibers, such as fibers providing from fabrics, textiles and/orindustrial wastes. More particularly, the process of the invention maybe used with PET fibers, such as PET fibers providing from fabrics,textile, or tires. Interestingly, the process of the invention allowsthe production of monomers and/or oligomers that may be furtherrecovered and/or reprocessed.

Advantageously, the process of the invention is used for degrading aplastic product comprising at least one polyester selected frompolyethylene terephthalate (PET); polytrimethylene terephthalate (PTT);polybutylene terephthalate (PBT); polyethylene isosorbide terephthalate(PEIT); polylactic acid (PLA)); polyhydroxyalkanoate (PHA) (such aspoly(3-hydroxybutyrate) (P(3HB)/PHB), poly(3-hydroxyvalerate)(P(3HV)/PHV), poly(3-hydroxyhexanoate) (P(3HHx)),poly(3-hydroxyoctanoate) (P(3HO)), poly(3-hydroxydecanoate) (P(3HD)),poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV)/PHBV),poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P(3HB-co-3HHx)/(PHBHHx)),poly(3-hydroxybutyrate-co-5-hydroxyvalerate) (PHB5HV),poly(3-hydroxybutyrate-co-3-hydroxypropionate) (PHB3HP),polyhydroxybutyrate-co-hydroxyoctonoate (PHBO),polyhydroxybutyrate-co-hydroxyoctadecanoate (PHBOd),poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-4-hydroxybutyrate)(P(3HB-co-3HV-co-4HB))); polybutylene succinate (PBS), polybutylenesuccinate adipate (PBSA), polybutylene adipate terephthalate (PBAT),polyethylene furanoate (PEF), polycaprolactone (PCL), poly(ethyleneadipate) (PEA), polyethylene naphthalate (PEN),polycyclohexylenedimethylene terephthalate (PCT), poly ethylenesuccinate (PES), poly(butylene succinate-co-terephthalate) (PBST),poly(butylene succinate/terephthalate/isophthalate)-co-(lactate)(PBSTIL) and blends/mixtures of these polymers.

Preferably, the process of the invention is used for degrading a plasticproduct comprising at least one thermoplastic polyester, preferablyselected from polyethylene terephthalate (PET); polytrimethyleneterephthalate (PTT); polybutylene terephthalate (PBT); polyethyleneisosorbide terephthalate (PEIT); polylactic acid (PLA));polyhydroxyalkanoate (PHA) (such as poly(3-hydroxybutyrate)(P(3HB)/PHB), poly(3-hydroxyvalerate) (P(3HV)/PHV),poly(3-hydroxyhexanoate) (P(3HHx)), poly(3-hydroxyoctanoate) (P(3HO)),poly(3-hydroxydecanoate) (P(3HD)),poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV)/PHBV),poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P(3HB-co-3HHx)/(PHBHHx)),poly(3-hydroxybutyrate-co-5-hydroxyvalerate) (PHB5HV),poly(3-hydroxybutyrate-co-3-hydroxypropionate) (PHB3HP),polyhydroxybutyrate-co-hydroxyoctonoate (PHBO),polyhydroxybutyrate-co-hydroxyoctadecanoate (PHBOd),poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-4-hydroxybutyrate)(P(3HB-co-3HV-co-4HB))); polybutylene succinate (PBS), polybutylenesuccinate adipate (PBSA), polybutylene adipate terephthalate (PBAT),polyethylene furanoate (PEF), polycaprolactone (PCL), poly(ethyleneadipate) (PEA), polyethylene naphthalate (PEN),polycyclohexylenedimethylene terephthalate (PCT), poly ethylenesuccinate (PES), poly (butylene succinate-co-terephthalate) (PBST),poly(butylene succinate/terephthalate/isophthalate)-co-(lactate)(PBSTIL) and blends/mixtures of these polymers.

In a particular embodiment, the process of the invention is used fordegrading plastic fibers comprising at least one polyester, andpreferably at least PET or PLA.

In a particular embodiment, the plastic product comprises at least twodifferent polymers, such as at least two polyesters. More generally, theplastic products targeted by the process of the invention may comprisedifferent kinds of polymers, including synthetic polymers, derived frompetrochemicals, or biobased sourced. As an example, the plastic productcomprises at least one polyester and further comprises polymers otherthan a polyester, such as polyamides, polyolefins or vinyl polymers(such as polyethylene, polypropylene, polystyrene, polyvinyl chloride,ethylene vinyl acetate, ethylene vinyl alcohol, or polyvinyl alcohol),rubber, wood or wood compounds such as lignin, cellulose orhemi-cellulose, and starch and derivatives thereof. As another example,the plastic product may comprise at least one polyester and furthercomprises an additional component such as metal compounds (such asaluminum, aluminum oxide, titanium, titanium oxide, nickel or chrome),mineral compounds (such as silica or silicon dioxide, glass, or mica),glass compounds, natural or synthetic fibers (such as carbon fibers,flax fibers, hemp fibers, wood fibers, paper fibers, straw fibers, jutefibers, cotton fibers, viscose fibers, glass fibers, metal fibers,aramid fibers, boron fibers, or ceramic fibers), paper, and derivativesthereof.

In a preferred embodiment of the invention, the plastic productcomprises aromatic polyesters, such as polyethylene terephthalate and/orpolytrimethylene terephthalate. Advantageously, the plastic productcomprises or is constituted of PET, preferably semi-crystalline PET. Inthe context of the invention, the terms “Polyethylene terephthalate” or“Polyethylene terephthalate polymer”, also abbreviated “PET” or “PETE”,are used interchangeably and refer to a thermoplastic polymer resin ofthe polyester family, produced from monomers of monoethylene glycol(MEG) and dimethyl terephthalate (DMT) or purified terephthalic acid(PTA). PET may exist both in amorphous and in semi-crystalline states.In the context of the invention, homopolymers and copolymers of PET arealso encompassed. Examples of copolymers are polyethylene terephthalateglycol-modified (PETG), wherein cyclohexane dimethanol is added to thepolymer backbone in place of ethylene glycol, or polyethyleneterephthalate isophthalic acid-modified, wherein isophthalic acidreplaces some of the linkage of terephthalate units, or bi-axiallyoriented PET (BOPET), or oriented PET (OPET), etc.

In another embodiment, the plastic product comprises aliphaticpolyester, such as PLA, and more particularly semi-crystalline PLA.According to the invention, the terms “Polylactic acid” or “Polylacticacid polymer”, also abbreviated PLA, are used interchangeably and referto a thermoplastic polymer resin of the polyester family, produced frommonomers of lactic acid (D-lactic acid or L-lactic acid). PLA may existboth in amorphous and in semi-crystalline states. In the context of theinvention, homopolymers, copolymers or stereocomplexes of PLA are alsoencompassed such as poly(L-lactic acid) (PLLA), poly(D-lactic acid)(PDLA), poly(D,L-lactic acid) (PDLLA), or stereocomplex PLA (scPLA).

It is therefore an object of the invention to provide a process fordegrading a plastic product containing at least one polyester,comprising the steps of:

a. Amorphizing at least partially at least one polyester of the plasticproduct; and

b. Depolymerizing said at least partially amorphized polyester of theplastic product.

It is also another object of the invention to provide a method ofproducing monomers and/or oligomers from a plastic product comprising atleast a polyester, comprising submitting the plastic product to anamorphization step to amorphize at least partially a polyester of theplastic product, and to a depolymerization step of said polyester of theplastic product, wherein the depolymerization step comprises exposingthe plastic product to a depolymerase. According to the invention, thedepolymerase is advantageously selected from the group consisting of acutinase, a lipase, a protease, a carboxylesterase, ap-nitrobenzylesterase, an esterase, a scl-PHA depolymerase, a mcl-PHAdepolymerase, a PHB depolymerase.

It is a particular object of the invention to provide a process fordegrading a plastic product containing PET, comprising the steps of:

a. Amorphizing at least partially PET of the plastic product bysubmitting the plastic product to a temperature above 170° C.,preferably above 185° C., more preferably above 200° C., even morepreferably above 220° C., 240° C., 245° C., 250° C., 255° C., 260° C.,265° C.; and then by submitting the plastic product to a temperaturebelow 80° C., preferably below 65° C., more preferably below 10° C.; and

b. Depolymerizing PET of the plastic product by contacting the plasticproduct to a depolymerase, preferably a cutinase.

It is another particular object of the invention to provide a processfor degrading a plastic product containing PLA, comprising the steps of:

a. Amorphizing at least partially PLA of the plastic product bysubmitting the plastic product to a temperature above 110° C.,preferably above 160° C., more preferably above 170° C.; and then bysubmitting the plastic product to a temperature below 85° C., preferablybelow 55° C., more preferably below 10° C.; and

b. Depolymerizing PLA of the plastic product by contacting the plasticproduct to a depolymerase, preferably a protease.

It is therefore an object of the invention to provide a method forproducing terephthalic acid and/or ethylene glycol and/ormethyl-2-hydroxyethyl terephthalate (MHET) and/or bis(2-hydroxyethyl)terephthalate (BHET) and/or 2-hydroxyethyl benzoate (HEB) and/ordimethyl terephthalate (DMT), from a plastic product comprising PET,wherein the plastic product is submitted to an amorphization step toamorphize at least partially PET of the plastic product, and to adepolymerising step of the PET of the plastic product, wherein thedepolymerizing step comprises exposing the plastic product to acutinase.

It is therefore another object of the invention to provide a method forproducing lactic acid, from a plastic product comprising PLA, whereinthe plastic product is submitted to an amorphization step to amorphizeat least partially PLA of the plastic product, and to a depolymerisingstep of the PLA of the plastic product, wherein the depolymerizing stepcomprises exposing the plastic product to a protease.

It is also another object of the invention to provide a process ofdegrading a plastic article further comprising a step of purification ofthe monomers and/or oligomers resulting from the step ofdepolymerization. Monomers and/or oligomers resulting from thedepolymerization may be recovered, sequentially or continuously. Asingle type of monomer and/or oligomers or several different types ofmonomers and/or oligomers may be recovered, depending on the polymersand/or the starting plastic articles.

It is a further object of the invention to provide a method forrecycling a plastic product comprising at least one polyester,comprising subjecting successively said at least one polyester toamorphization and depolymerization, and recovering monomers and/oroligomers.

The recovered monomers and/or oligomers may be purified, using allsuitable purifying method and conditioned in a re-polymerizable form.Examples of purifying methods include stripping process, separation byaqueous solution, steam selective condensation, filtration andconcentration of the medium after the bioprocess, separation,distillation, vacuum evaporation, extraction, electrodialysis,adsorption, ion exchange, precipitation, crystallization, concentrationand acid addition dehydration and precipitation, nanofiltration, acidcatalyst treatment, semi continuous mode distillation or continuous modedistillation, solvent extraction, evaporative concentration, evaporativecrystallization, liquid/liquid extraction, hydrogenation, azeotropicdistillation process, adsorption, column chromatography, simple vacuumdistillation and microfiltration, centrifugation, ultrafiltration,combined or not.

Particularly, the invention provides a process of degrading a plasticproduct comprising PET wherein preferred recovered monomers are selectedfrom monoethylene glycol and terephthalic acid, and preferred oligomersare selected from methyl-2-hydroxyethyl terephthalate (MHET),bis(2-hydroxyethyl) terephthalate (BHET), 2-hydroxyethyl benzoate (HEB)and dimethyl terephthalate (DMT).

Particularly, the invention provides a process of degrading a plasticproduct comprising PLA wherein preferred recovered monomers are selectedfrom lactic acid, particularly D-lactic acid or L-lactic acid.

In a preferred embodiment, the repolymerizable monomers and/or oligomersmay then be reused to synthesize polymers, preferably polyesters.Advantageously, polymers of same nature are repolymerized. However, itis possible to mix the recovered monomers and/or oligomers with othermonomers and/or oligomers, in order to synthesize new copolymers.Initiators may be added to the monomers/oligomers solution to favor thepolymerization reaction. One skilled in the art may easily adapt theprocess parameters to the monomers/oligomers and the polymers tosynthesize.

In addition or alternatively, a step of recovering the non-depolymerizedpolymers is further performed after the step of depolymerization.Particularly, such polymers may be constituted of the crystalline partof the polyester originally submitted to the step of depolymerizationand/or different polymers constituting the plastic article. Examples ofrecovering methods include filtration, microfiltration, separation,solvent extraction, solvent solubilization and evaporation,liquid/liquid extraction, decantation, centrifugation.

Further aspects and advantages of the invention will be disclosed in thefollowing examples, which should be considered as illustrative and donot limit the scope of this application. The following is a descriptionof the present invention, including preferred embodiments thereof givenin general terms. The present invention is further exemplified in thedisclosure given under the heading “Examples” herein below, whichprovides experimental data supporting the invention and means ofperforming the invention.

EXAMPLES Example 1—Process of Degrading a Plastic Product ContainingPET: Volvic® Bottles

A) Amorphizing Step

Volvic® water bottles were collected after use. Caps and adhesive labelswere removed. Then the bottles were ground into flakes using a Rapid 150Delta Tech granulator. A first sample (VB1) was collected.

The initial degree of crystallinity (Xc) of flakes was estimated using aMettler Toledo DSC 3 with heating rate of 10° C./min. The measuredinitial crystallinity was 26%. The different temperatures characterizingVB1 were also measured:

-   -   Glass transition temperature—Tg=67° C.,    -   Cold crystallization temperature—Tcc=134° C.    -   Melting temperature—Tm=250° C.

The amorphizing step was performed using a twin screw extruder LeistritzZSE 18 MAXX, which comprises nine successive heating zones (Z1-Z9)wherein the temperature may be independently controlled and regulated,and a head (Z10).

In a first embodiment, Volvic® bottle flakes VB1 were introduced in theprincipal hopper (before Z1). Temperature profile all along the screw isdescribed in Table 1. The screw speed rate was 30 rpm.

TABLE 1 Temperature profile of extruder used for VB2 and VB3 Zone Z10 Z1Z2 Z3 Z4 Z5 Z6 Z7 Z8 Z9 (head) T° C. 170° C. 230° C. 250° C. 260° C.270° C. 270° C. 270° C. 260° C. 250° C. 250° C.

The molten polymer arrived in the screw head (Z10) comprising a dieplate with one hole of 3.5 mm and was immediately immersed in a 2 m longcold water bath filled with a mix of water and crushed ice. Resultingbath temperature was about 5° C.

The resulting extrudate was granulated into fine solid pellets <3 mm,and a sample VB2 was collected. The degree of crystallinity of VB2,measured by DSC, was 9%.

In a second embodiment, the amorphizing step, as disclosed above (withsame extruder parameters and cooling conditions) was performed on VB1,with the addition of water. More particularly, 10% of water by totalweight were added directly to Volvic® bottle flakes, then mixed beforeintroducing in the principal hopper (before Z1).

The resulting extrudate was granulated to fine solid pellets <3 mm, anda sample VB3 was collected.

The degree of crystallinity of VB3, measured by DSC, was 11%.

In a third embodiment, the amorphizing step was performed on VB1 withsame extruder, same temperature profile as shown in table 1 and samecooling conditions, but with a different speed rate of 60 rpm. Theresulting extrudate was granulated to fine solid pellets <3 mm, and asample VB4 was collected. The degree of crystallinity of VB4, measuredby DSC, was 12%.

In a fourth embodiment, the amorphizing step was performed on VB1 withsame extruder, same temperature profile as shown in table 1, samecooling conditions, a speed rate of 60 rpm and the addition to flakes of10% of water by total weight. The resulting extrudate was granulated tofine solid pellets <3 mm, and a sample VB5 was collected. The degree ofcrystallinity of VB5, measured by DSC, was about 12%.

In a fifth embodiment, the amorphizing step was performed on VB1 withsame extruder, same temperature profile as shown in table 1, samecooling conditions, a speed rate of 60 rpm, and the addition to flakesof 1% of EG by total weight. The resulting extrudate was granulated tofine solid pellets <3 mm, and a sample VB6 was collected. The degree ofcrystallinity of VB6, measured by DSC, was 16%.

B) Depolymerization Step

a) Enzymatic Depolymerization of Samples VB1, VB2 and VB3:

The subsequent depolymerization, on VB1, VB2 and VB3, was performed witha LC-cutinase produced from recombinant expression in Escherichia coli(Sulaiman et al., Appl Environ Microbiol. 2012 March).

For each VB1, VB2 and VB3 samples, 100 mg of samples were respectivelyweighted and introduced in a dialysis tubing.

1 mL of LC-cutinase at 0.1 mg/mL in 0.1 M potassium phosphate at pH 8was added in the dialysis tubing before closing it. The dialysis tubingwas then introduced in a glass bottle containing 49 mL of 0.1 Mpotassium phosphate buffer pH 8.

The depolymerization was started by incubating each sample at 70° C. and150 rpm in a Max Q 4450 incubator (Thermo Fisher Scientific, Inc.Waltham, Mass., USA).

Aliquots of 150 μL of buffer were sampled regularly. If necessary,samples were diluted in 0.1 M potassium phosphate buffer pH 8. Then, 150μL of methanol and 6.5 μL of HCl 6 N were added to 150 μL of sample.

After mixing and filtering on 0.45 μm syringe filter, samples wereanalyzed by Ultra High Pressure Liquid Chromatography (UHPLC) to monitorthe liberation of terephthalic acid (TA), MHET and BHET. Chromatographysystem used was an Ultimate 3000 UHPLC system (Thermo Fisher Scientific,Inc. Waltham, Mass., USA) including a pump module, an autosampler, acolumn oven thermostated at 25° C., and an UV detector at 240 nm. Thecolumn used was a Discovery® HS C18 HPLC Column (150×4.6 mm, 5 μm,equipped with precolumn, Supelco, Bellefonte, USA). Eluents were 10 mMH₂SO₄ (eluent A), ultra-pure water (eluent B) and methanol (eluent C).TA, MHET and BHET were separated using a gradient of MeOH in water at 1mM of H₂SO₄. Injection was 20 μL of sample. TA, MHET and BHET weremeasured according to standard curves prepared from commercial TA andBHET and in house synthesized MHET in the same conditions than samples.

The percentage of hydrolysis of Volvic® bottle samples VB1, VB2 and VB3were calculated based on the ratio of molar concentration at a giventime (TA+MHET+BHET) versus the total amount of TA contained in theinitial sample. Results of depolymerization are shown in FIG. 1.

The initial rates of enzymatic depolymerization of amorphized samplesVB2 and VB3 were improved 8.2 and 9.8 times respectively compared to thehydrolysis initial rate of the non-amorphized VB1. At the end of thereaction, 88% and 84% of amorphized samples VB2 and VB3, respectively,were degraded by the enzyme, whereas only 12% of VB1 was enzymaticallydegraded.

b) Enzymatic Depolymerization of Samples VB4, VB5 and VB6

The same procedures of samples depolymerization (depolymerase used, pH,T°, agitation, etc.) and degradation analysis as the one described forsamples VB1, VB2 and VB3, were applied to samples VB4, VB5 and VB6. Onlythe temperature during the depolymerization step was different, i.e. 65°C. instead of 70° C.

The percentage of hydrolysis of Volvic® bottle samples VB1, VB4, VB5 andVB6 were calculated, as previously described. Results ofdepolymerization are shown in FIG. 2.

The initial rates of enzymatic depolymerization of amorphized samplesVB4, VB5 and VB6 were improved 3.6 times, 4.8 times and 8.4 timesrespectively, compared to the hydrolysis initial rate of thenon-amorphized sample VB1. At the end of the reaction, 82%, 94% and 47%of amorphized samples VB4, VB5 and VB6 were enzymatically degraded,respectively, whereas only 12% of crystalline Volvic® sample VB1 wereenzymatically degraded.

c) Enzymatic Depolymerization of Samples VB1 and VB5 Using HiC Cutinase

The subsequent depolymerization, on VB1 and VB5, was performed with HiCcutinase (Humicola insolens cutinase accession number A0A075B5G4 inUniprot) produced from recombinant expression in Yarrowia lipolytica.

A synthetic gene optimized for expression in Yarrowia lipolytica andencoding 194 amino acid mature HiC was obtained from Genscript. Thissequence was cloned in vector JMP62UraTef downstream of the sequenceencoding signal peptide and prodomain (33 N-terminal amino acids) oflipase 2 from Yarrowia lipolytica (accession number Q9P8F7). The vectoris a derivative of a previously described vector (Nicaud et al (2002)FEMS Yeast Res 2(3):371-379). This vector contains the Y. lipolytica TEFpromoter and URA3ex excisable selection marker, which are flanked byloxP sites and a Zeta fragment that serves as the homologous integrationsite.

Vectors were verified by DNA sequencing (GATC Biotechy). Vector wasdigested using NotI, thus generating a linear DNA with Zeta sequences atboth extremities, and purified. The linear DNA fragment was introducedinto the Zeta docking platform of Y. lipolytica JMY1212 Zeta (Bordes etal. (2007) J Microbiol Methods 70(3):493-502) using the lithium acetatemethod (Duquesne et al. (2012) Methods Mol Biol 861:301-312). Enzymeswere produced in YT2D5 medium (1% w/v yeast extract, 2% w/v tryptone, 5%w/v glucose and 100 mM phosphate buffer, pH 6.8) for 48 h. Culture washarvested and supernatant was collected. Culture supernatant wasfiltered on 0.2 μm and concentrated using a dialysis tube Amicon Ultrawith a cut off of 3 kDa. HiC concentration in the concentrated extractwas then estimated using Bradford method.

For each VB1 and VB5 samples, 100 mg of samples were respectivelyweighted and introduced in a dialysis tubing.

1 mL of HiC cutinase at 0.65 mg/mL in 0.1 M potassium phosphate at pH 8was added in the dialysis tubing before closing it. The dialysis tubingwas then introduced in a glass bottle containing 49 mL of 0.1 Mpotassium phosphate buffer pH 8. The depolymerization was started byincubating each sample at 60° C. and 150 rpm in a Max Q 4450 incubator(Thermo Fisher Scientific, Inc. Waltham, Mass., USA).

The same procedures of samples degradation analysis as the one describedin a) and b) were applied.

The percentage of hydrolysis of Volvic® bottle samples VB1 and VB5 werecalculated, as previously described. After 70 hours of reaction, theamorphized sample VB5 shows a degradation rate 173% higher than the VB1sample.

Example 2—Process of Degrading a Plastic Product Containing PET: OpaqueMilk Bottles

A) Amorphization by Extrusion of PET Flakes from Opaque Pâturages™ MilkBottles

Opaque milk bottles from Pâturages™ were collected and washed after use.Caps and adhesive labels were removed. Then, the bottles were groundinto flakes using a Rapid 150 Delta Tech granulator. A sample from theobtained flakes was micronized using an Ultra Centrifugal Mill ZM 200system to a fine powder <500 μm size. This first sample was named MB1.The initial degree of crystallinity (Xc) of MB1 powder was estimatedusing a Mettler Toledo DSC 3 with heating rate of 10° C./min. Themeasured initial crystallinity was 27%. The different temperaturescharacterizing MB1 were also measured: Tg=66° C., Tcc=120° C. andTm=244° C.

The amorphizing step was performed using the same win screw extruderLeistritz ZSE 18 MAXX, as the one described in Example 1.

In a first embodiment, milk bottle flakes were introduced in theprincipal hopper (before Z1 zone). Temperatures were increased up to270° C. in Z5, Z6 and Z7 to obtain a molten PET in the die head (seetable 1). The screw speed rate set was 30 rpm.

The molten polymer arrived in the screw head (Z10) comprising a dieplate with one hole of 3.5 mm and was immediately immersed in a 2 m longcold water bath filled with a mix of water and crushed ice. Resultingbath temperature was about 5° C. The resulting extrudate was granulatedto fine solid pellets <3 mm, and was micronized using an UltraCentrifugal Mill ZM 200 system to a fine powder <500 μm size. Thissample was designated sample MB2. The degree of crystallinity of MB2,measured by DSC, was less than 1%.

In a second embodiment, the amorphizing step was performed on milkbottle flakes with same extruder, same temperature profile as table 1,the same cooling conditions, but with a speed rate of 60 rpm. Theresulting extrudate was granulated to fine solid pellets <3 mm and wasmicronized using an Ultra Centrifugal Mill ZM 200 system to a finepowder <500 μm size. This sample was designated sample MB3. The degreeof crystallinity of MB3, measured by DSC, was 4%.

In a third embodiment, the amorphizing step as disclosed above wasperformed on milk bottle flakes with the same temperature profile astable 2, a speed rate of 60 rpm, with addition of water. Moreparticularly, 20% by weigh of water based on the total weight were addeddirectly to the flakes, then mixed before introduction in the principalhopper (before Z1). The same cooling conditions as the first embodimentwere used. The resulting extrudate was granulated to fine solid pellets<3 mm, and a sample was collected and micronized using an UltraCentrifugal Mill ZM 200 system to a fine powder <500 μm size. Thissample was designated sample MB4. The degree of crystallinity of MB4,measured by DSC, was 1%.

B) Depolymerization of Amorphized Milk Bottles Using a Cutinase

The subsequent depolymerization, on MB1, MB2, MB3 and MB4, was performedwith a LC-cutinase produced from recombinant expression in Escherichiacoli (Sulaiman et al., Appl Environ Microbiol. 2012 March), using thesame material and method as exposed in Example 1.

The hydrolysis of milk bottle samples MB1, MB2, MB3 and MB4 werecalculated based on TA, MHET and BHET released as previously describedin Example 1. Results of depolymerization are shown in FIG. 3.

Initial rate of enzymatic depolymerization was improved 3.2 times, 4.6times and 10 times for amorphized samples MB3, MB2 and MB4 respectively,in comparison with micronized milk bottle (sample MB1). At the end ofthe reaction, 86%, 88% and 89% of amorphized samples MB3, MB2 and MB4were degraded by the enzyme, respectively, whereas only 33% ofcrystalline milk bottle sample MB1 were enzymatically degraded.

Another subsequent depolymerization, on MB1 and MB4, was performed withHiC cutinase produced from recombinant expression in Yarrowia lipolyticausing the same material and method, same procedures of samplesdepolymerization and degradation analysis as exposed in Example 1B)c).

The percentage of hydrolysis of opaque Pâturages™ milk bottles samplesMB1 and MB4 were calculated, as previously described. After 70 hours ofreaction, the amorphized sample MB4 shows a degradation rate 152% higherthan the MB1 sample.

Example 3—Process of Degrading a Plastic Product Containing PET:Cristaline™ Water Bottles

A) Amorphization by Extrusion of PET Flakes from Cristaline™ WaterBottles

Cristaline™ water bottles were collected after use. Caps and adhesivelabels were removed. Then the bottles were ground into flakes using aRapid 150 Delta Tech granulator, a sample from flakes was micronizedusing an Ultra Centrifugal Mill ZM 200 system to a fine powder <500 μmsize, this sample was named CB1. The initial degree of crystallinity(Xc) of CB1 powder was estimated using a Mettler Toledo DSC 3 withheating rate of 10° C./min. The measured initial crystallinity was 33%.The different temperatures characterizing CB1 were also measured:Tg=70.5° C., Tcc=128° C., Tf=242° C.

The amorphizing step was performed using the same twin screw extruderLeistritz ZSE 18 MAXX, as the one described in Example 1 and 2.Cristaline™ bottle flakes were introduced in the principal hopper(before Z1 zone). Temperatures were increased up to 270° C. in Z5, Z6and Z7 to obtain a molten PET in the die head (see table 1). The screwspeed rate set was 30 rpm.

The molten polymer arrived in the screw head (Z10) comprising a dieplate with one hole of 3.5 mm and was immediately immersed in a 2 m longcold water bath filled with a mix of water and crushed ice. Resultingbath temperature was about 5° C. The resulting extrudate was granulatedto fine solid pellets <3 mm and designated, a sample from the obtainedpellets was micronized using an Ultra Centrifugal Mill ZM 200 system toa fine powder <5001 μm size, this sample was named CB2. The degree ofcrystallinity of amorphized and micronized sample CB2 was 2.7%.

B) Enzymatic Depolymerization of Amorphized Cristaline™ Water Bottles ina Reactor

Two Minibio 500 bioreactors (Applikon Biotechnology B.V., Delft, TheNetherlands) were started with 10 g of samples CB1 or CB2 and 100 mL of10 mM potassium phosphate buffer pH 8 containing 10 mg of LC-cutinase.Agitation was set at 250 rpm using a marine impeller. Bioreactors werethermostated at 65° C. by immersing them in an external water bath. pHwas regulated at 8 by addition of KOH at 3 M. The different parameters(pH, temperature, agitation, addition of base) were monitored thanks toBioXpert software V2.95.

Aliquots of reaction mix were sampled regularly and prepared accordingto example 1 to performed the measurement.

The percentage of hydrolysis of Cristaline™ bottle samples CB1 and CB2were calculated based on TA, MHET and BHET released as previouslydescribed in Example 1. Results of depolymerization are shown in FIG. 4.

At the end of the reaction, 90.5% of amorphized Cristaline™ bottlesample CB2 was degraded by the enzyme, whereas only 18% of crystallineCristaline™ bottle sample CB1 were enzymatically degraded.

Another subsequent depolymerization, on CB1 and CB2 was performed withHiC cutinase produced from recombinant expression in Yarrowia lipolyticausing the same material and method, same procedures of samplesdepolymerization and degradation analysis as exposed in Example 1B)c).

The percentage of hydrolysis of Cristaline™ bottle samples CB1 and CB2were calculated, as previously described. After 70 hours of reaction,the amorphized sample CB2 shows a degradation rate 570% higher than theCB1 sample.

Example 4—Process of Degrading a Plastic Product Containing PLA: BioWareCups

A) Amorphization by Extrusion of PLA Flakes from BioWare Cups

BioWare cups were collected then grounded into flakes using a Rapid 150Delta Tech granulator. This first sample was named BC1. The initialdegree of crystallinity (Xc) of flakes was estimated using a MettlerToledo DSC 3 with heating rate of 10° C./min. The measured initialcrystallinity was 24.2%.

The different temperatures characterizing BC1 were also measured: Tg=64°C., Tcc=113° C., Tm=148° C.

The amorphizing step was performed using the same twin screw extruderLeistritz ZSE 18 MAXX, of example 1, but with a different temperatureprofile (see table 2 below).

In a first embodiment, BioWare cups flakes BC1 were introduced in theprincipal hopper (before Z1 zone). The screw speed rate set was 60 rpm.

TABLE 2 Temperature profile of extruder used for BC2, BC3 Zone Z10 Z1 Z2Z3 Z4 Z5 Z6 Z7 Z8 Z9 (head) T° C. 180° C. 180° C. 180° C. 180° C. 170°C. 170° C. 170° C. 170° C. 170° C. 170° C.

The molten polymer arrived in the screw head (Z10) comprising a dieplate with one hole of 3.5 mm and was immediately immersed in a 2 m longcold water bath, filled with a mix of water and crushed ice. Resultingbath temperature was about 5° C.

The resulting extrudate was granulated to fine solid pellets <3 mm anddesignated sample BC2. The degree of crystallinity of amorphized sampleBC2 was 2%.

In a second embodiment, the amorphizing step as disclosed above (withsame extruder parameters and cooling conditions) was performed on BC1,with the addition of 10% of water by total weight to Bioware cupsflakes. The mixture was then mixed before introducing in the principalhopper (before Z1).

The resulting extrudate was granulated to fine solid pellets <3 mm, anda sample BC3 was collected.

The degree of crystallinity of BC3, measured by DSC, was 7%.

B) Enzymatic Depolymerization of Amorphized PLA BioWare Cups

BC1, BC2 and BC3 were immersed in liquid nitrogen and were micronizedusing an Ultra Centrifugal Mill ZM 200 system to a fine powder <500 μmsize, then 100 mg of each micronized sample were weighted and introducedin a dialysis tubing. 3 mL of Savinase® 16 L diluted to 1/100 in 0.1 MTris buffer pH 9.5 was added in the dialysis tubing before closing it.The dialysis tubing was then introduced in a plastic bottle containing50 mL of 0.1 M Tris buffer pH 9.5. The depolymerization was started byincubating each sample at 45° C. and 150 rpm in a Infors HT MultitronPro incubation shaker. Aliquots of 1 mL of buffer were sampled regularlyand filtered on 0.22 μm syringe filter, samples were analyzed by HighPressure Liquid Chromatography (HPLC) with an Aminex HPX-87H column tomonitor the liberation of lactic acid (LA) and lactic acid dimer (DP2).Chromatography system used was an Ultimate 3000 UHPLC system (ThermoFisher Scientific, Inc. Waltham, Mass., USA) including a pump module, anautosampler, a column oven thermostated at 50° C., and an UV detector at220 nm. Eluent was 5 mM H₂SO₄. Injection was 20 μL of sample. LA weremeasured according to standard curves prepared from commercial LA. DP2were measured in equivalent LA, by applying 0.8 factor to the standardcurve of LA.

Hydrolysis of BioWare cups samples BC1, BC2 and BC3 were calculatedbased on LA and dimer of LA released. Results of depolymerization areshown in Table 3 below.

TABLE 3 Depolymerization rate of PLA BioWare cups before (BC1) and afteramorphization according to the invention (BC2 and BC3) after 7 h ofreaction Degradation rate in Degree of Degradation rate base 100compared Samples crystallinity after 7 hours to BC1 BC1 24% 34% 100 BC22% 44% 129 BC3 7% 41% 121

After seven hours, 44% and 41% of amorphized samples BC2 and BC3,respectively, were degraded by the enzyme, whereas only 34% of BC1 wasenzymatically degraded.

The invention claimed is:
 1. A process for degrading a plastic productcomprising at least one semi-crystalline thermoplastic polyestercomprising the steps of: a) amorphizing at least partially said at leastone semi-crystalline thermoplastic polyester of the plastic product byheating the plastic product at a temperature above the meltingtemperature (Tm) of said semi-crystalline thermoplastic polyester, andfurther cooling the plastic product at a temperature below thecrystallization temperature (Tc) of said semi-crystalline thermoplasticpolyester, and b) depolymerizing said at least partially amorphizedpolyester of the plastic product by contacting the plastic product witha depolymerase able to depolymerize said at least partially amorphizedpolyester into monomers and/or oligomers.
 2. The process of claim 1,wherein the cooling of said plastic product comprises cooling theplastic product to a temperature below the glass transition temperature(Tg) of said semi-crystalline thermoplastic polyester of the plasticproduct.
 3. The process of claim 1, wherein the step of amorphizingfurther comprises adding at least one degrading agent.
 4. The process ofclaim 3, wherein the degrading agent is selected from the groupconsisting of water, monomers of a polyester of the plastic product,metal alkoxides, alcohol and plasticizers.
 5. The process of claim 1,wherein the step of amorphizing is performed by use of an extruder. 6.The process of claim 1, wherein the step of amorphizing leads to atleast partially amorphized polyester with at most 30% of crystallinity.7. The process of claim 1, wherein the depolymerising step comprisescontacting the plastic product with at least one microorganismexpressing and excreting a depolymerase able to depolymerize said atleast partially amorphized polyester into monomers and/or oligomers. 8.The process of claim 1, further comprising recovering oligomers and/ormonomers resulting from depolymerisation of said at least partiallyamorphized polyester of the plastic product.
 9. The process of claim 8,wherein the recovered oligomers and/or monomers are further purified.10. The process of claim 1, further comprising a preliminarydepolymerising step performed prior to the amorphizing step.
 11. Theprocess of claim 1, comprising a pretreatment step to modify the plasticproduct mechanically and/or physically and/or chemically and/orbiologically.
 12. The process of claim 11, wherein said pretreatmentstep is performed before the amorphizing step and/or before thedepolymerising step.
 13. The process of claim 1, wherein the plasticproduct comprises semi-crystalline polyesters, selected frompolyethylene terephthalate (PET), polytrimethylene terephthalate (PTT),polybutylen terephthalate (PBT), polyethylene isosorbide terephthalate(PEIT), polylactic acid (PLA), polyhydroxy alkanoate (PHA), polybutylenesuccinate (PBS), polybutylene succinate adipate (PBSA), polybutyleneadipate terephthalate (PBAT), polyethylene furanoate (PEF),polycaprolactone (PCL), poly(ethylene adipate) (PEA), polybutylenesuccinate terephthalate (PBST), polyethylene succinate (PES),poly(butylene succinate/terephthalate/isophthalate)-co-(lactate)(PBSTIL) and blends/mixtures of these materials.
 14. The process ofclaim 1, wherein the plastic product comprises semi-crystallinepolyethylene terephthalate and/or semi-crystalline polylactic acid. 15.The process of claim 13, wherein the depolymerizing step is performed bycontacting the plastic product with a depolymerase selected from thegroup consisting of cutinases, proteases, lipases, carboxylesterases andesterases.
 16. The process of claim 1, wherein the plastic productcomprises at least PET, and the amorphizing step comprises heating theplastic product to a temperature above 245° C., then cooling the plasticproduct to a temperature between 5° C. and 65° C.
 17. The process ofclaim 1, wherein the plastic product comprises at least PET, and thedepolymerizing step comprises submitting the plastic product to acutinase.
 18. The process of claim 1, wherein the plastic productcomprises at least PET, and the amorphizing step comprises exposing theplastic product to a temperature above 245° C., then exposing theplastic product to a temperature comprised between 5° C. and 65° C., andthe depolymerising step comprises contacting the plastic product to acutinase.
 19. A method of producing monomers and/or oligomers from aplastic product containing at least one semi-crystalline thermoplasticpolyester, comprising submitting the plastic product to an amorphizationstep to amorphize at least partially said semi-crystalline thermoplasticpolyester of the plastic product, wherein the amorphization stepcomprises heating the plastic product to a temperature above the meltingtemperature (Tm) of said semi-crystalline thermoplastic polyester andfurther cooling the product to a temperature below the crystallizationtemperature (Tc) of said semi-crystalline thermoplastic polyester, andto a depolymerising step to depolymerise said at least partiallyamorphized polyester of the plastic product, wherein the depolymerizingstep comprises contacting the plastic product with a depolymerase ableto degrade said at least partially amorphized polyester.
 20. The methodof claim 19, wherein the plastic product comprises polyethyleneterephthalate, the depolymerizing step comprising exposing the plasticproduct to a cutinase.
 21. A process for degrading a plastic productcomprising at least one semi-crystalline thermoplastic polyester thathas been previously amorphized by heating the plastic product to atemperature above the melting temperature (Tm) of said semi-crystallinethermoplastic polyester and further cooling the plastic product to atemperature below the crystallization temperature (Tc) of saidsemi-crystalline thermoplastic polyester comprising contacting saidamorphized plastic product with a depolymerase able to degrade saidpreviously amorphized polyester.